Increase In Stored Energy Research Articles

Effects of ultrasonic shot peening process on the microstructure and mechanical properties of nickel-based superalloys formed by selective laser melting

Selective laser melting (SLM) is an attractive additive manufacturing technique for fabricating high-performance superalloys engineering components. Unfortunately, these as-built parts generally exhibit unsatisfied mechanical properties because of their natural thermal residual stress and non-equilibrium microstructures. Ultrasonic shot peening (USP) can effectively inhibit defect expansion and even close pores, thereby improving the mechanical properties of alloys. In this study, the internal defects, residual stress and microhardness redistribution, tensile properties, as well as microstructural response of the GH3230 alloy treated by different ultrasonic peening time are systematically studied. USP treatment induces a significant carbides fragmentation and synthesizes surface gradient heterogeneous structure, which displays a microstructure gradient in grain size, carbides size and dislocation density from surface to core. Long-time USP treatment induces work softening of GH3230 alloys. The work softening mechanism of the GH3230 alloys after long-time USP treatment is ascribed to the increase of surface temperature and high stored strain energy. Both the microhardness and residual compressive stress in the softened region of GH3230 alloys are reduced. Work softening effect increases the surface plasticity of the GH3230 sample, which induces deeper gradient structure. The various strengthening mechanisms of gradient heterogeneous structures, as well as the multiple effects of hetero deformation induced (HDI) hardening, and densification strengthening are responsible for achieving strength-ductility synergy. The research findings provide new insights based on USP for improving the mechanical properties of heterogeneous superalloys engineering components.

The Evolutionary Theory along the Phylogenetic Tree of Unicellular Organisms

In parallel to the advancement of molecular biology suggesting the evolutionary route from the RNA world to the DNA-RNA-protein world through the RNA-protein world, the analysis on the nucleotide base changes in ribosomal RNA genes revels that the divergence of prokaryote and eukaryote first occurred in the DNA-RNA-protein world but the divergence of present-day lineages in eukaryotes occurred after the ancestral eukaryote has acquired the mitochondria as the endosymbionts of O2-respiratory eubacteria. These results strongly suggest that the divergence of unicellular organisms is closely related with the drastic changes in cell contents such as the formation of ribosome, the generation of RNA genes, the conversion from the RNA genes to DNA genes, gene duplication or the endosymbiosis. In the present paper, such drastic changes in evolution of unicellular organisms are theoretically formulated on the basis of the concept of biological activity which consists of the acquired energy, stored energy and systematization. Upon the drastic change in cell contents, the biological activity of an organism is first lowered by the increase in stored energy, but it is gradually recovered as the systematization advances to increase the acquired energy overcoming the increased stored energy and negative entropy due to the systematization itself. Throughout this process, the divergence of new style organisms occurred utilizing new material and energy sources. Such evolutionary process will be explained in detail at the main divergence points in the phylogenetic tree. The relation of such drastic changes in evolution with Darwinian evolution is also clarified.

Coupling charge pump and BUCK circuits to efficiently enhance the output performance of triboelectric nanogenerator

Triboelectric nanogenerator (TENG) faces significant challenges in practical applications because of its low output charge density and high matching impedance, and the development of its energy management circuits is hindered by high initial device requirements, large circuit size and poor portability. In this work, we propose a simple, efficient and versatile energy management strategy that two-stage amplification of TENG output performance by coupling a charge pump circuit with a BUCK circuit. By implementing the energy management strategy, the charge output per cycle of an ordinary TENG can be increased by more than 40 times, resulting in a power density of 25.2 mWm−2 and a total energy transfer efficiency of exceeding 88% in constant mode. At a working frequency of 1 Hz, the TENG can charge a 1000 μF capacitor to 5.04 V in 240 s and store the energy of more than 12.72 mJ, of which represents an 848-fold increase in stored energy compared to using TENG directly. Remarkably, this TENG device exhibits exceptional an average power of 100.7 μW/Hz, setting a new record for devices with smaller TENG size (< 50 cm2) or limited PM circuit size (< 10 cm2). Moreover, an ordinary TENG can continuously power a wireless sensor by integrating the portable power management circuit, facilitating real-time wireless data transmission. This study is of great significance for the practical application of the TENG power supply in the sensor network of the Internet of Things and for expanding the application range of the TENG.

Developing high performance RF heating scenarios on the WEST tokamak

High power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53 s with stationary conditions in particular with respect to tungsten contamination. Transitions to H mode are observed, and H-modes lasting up to 4 s have been obtained. The increase in stored energy is weak since the power crossing the separatrix is close to the L–H threshold. Hot L mode plasmas (central temperature exceeding 3 keV) with a confinement time following the ITER L96 scaling law are routinely obtained. The weak aspect ratio dependence of this scaling law is confirmed. Tungsten accumulation is generally not an operational issue on WEST. Difficulty of burning through tungsten can prevent the discharge from accessing to a hot core plasma in the ramp-up phase, or can lead to rapid collapse of the central temperature when radiation is enhanced by a slight decrease of the temperature. Except a few pulses post-boronization, the plasma radiation is rather high (P rad/ P tot ∼ 50%) and is dominated by tungsten. This fraction does not vary as the RF power is ramped up and is quite similar in ICRH and/or LHCD heated plasmas. An estimate of the contribution of the RF antennas to the plasma contamination in tungsten is given.

A numerical investigation on the finned storage rotation effect on the phase change material melting process of latent heat thermal energy storage system

Latent Heat Thermal Energy Storage (LHTES) is one of the most significant ways to mitigate solar energy intermittency using Phase Change Material (PCM). In the present study, a novel simultaneous utilization of longitudinal fins and storage rotation techniques to reduce the charging time and increase the amount of energy stored is considered in a double-pipe heat exchanger by developing a two-dimensional numerical model. Seven main cases have been defined, and finally, an optimal case with the least complete melting time has been introduced. The results indicated that embedding the fin on the lower half of the fixed storage accelerates the melting process. Rotating the finned storage can further reduce the melting time by up to 18.5 %, and embedded fins in rotating storage trap the melted PCM and reduce the complete melting time by 70 %. Finally, it is observed that simultaneous use of storage rotation and embedded longitudinal full-scale fins can achieve a 72 % reduction in complete melting time and a 115 % increase in total cumulative stored energy, which is related to the optimal case. The optimal case has four fins with an angle difference of 90° and two vertical stop steps with an angle of 180°.

Phase-field investigation on the grain evolution and mechanical response during dynamic recrystallization of deforming tungsten

In this work, the microstructural evolution and mechanical response during tungsten’s dynamic recrystallization (DRX) processes were studied by multiphase-field simulations coupling a dislocation density model for plastic deformation. We found that the deforming tungsten could reach a dynamic balanced state characterized by converged stress-strain curve and average radius of refined grains. This balance is determined by the deformation temperature and strain rate, instead of the initial averaged grain size. When the deformation parameters change during DRX, the final dynamically balanced state is solely determined by the final values of deformation parameters, while irrelevant to the history of their changes. Moreover, we find that such dynamic balance is essentially caused by the offset effects of grain growth and grain nucleation. The former leads to the increase of stored plastic energy and grain size while the latter leads to the opposite effects. Finally, a novel constitutive equation considering initial grain size, temperatures and strain rate is established, and generally agrees well with experimental results for the DRX of tungsten. These results clarify the synchronous relationship between mechanical response and microstructure evolution, and could help us to predict and tailor the microstructures of deforming alloys.

Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiments

Analysis of ‘super H-mode’ experiments on DIII-D has put forward that high plasma toroidal rotation, not high pedestal, plays the essential role in achieving energy confinement quality H 98y2 ≫ 1 (Ding et al 2020 Nucl. Fusion 60 034001). Recently, super H-mode experiments with variable input torque have confirmed that high rotation shear discharges have very high levels of H 98y2 (>1.5), independent of the pedestal height, and that high pedestal discharges with low rotation shear have levels of H 98y2 only slightly above 1 (⩽1.2). Although some increase in stored energy with higher pedestal occurs, the energy confinement quality mainly depends on the toroidal rotation shear, which varies according to different levels of injected neutral beam torque per particle. Quasi-linear gyrofluid modeling achieves a good match of the experiment when including the E × B shear; without including plasma rotation, the modeling predicts a confinement quality consistent with the empirical observation of H 98y2 ∼ 1.2 at low rotation. Nonlinear gyrokinetic transport modeling shows that the effect of E × B turbulence stabilization is far larger than other mechanisms, such as the so-called hot-ion stabilization (T i/T e) effect. Consistent with these experimental and modeling results are previous simulations of the ITER baseline scenario using a super H-mode pedestal solution (Solomon et al 2016 Phys. Plasmas 23 056105), which showed the potential to exceed the Q = 10 target if the pedestal density could be increased above the Greenwald limit. A close look at these simulations reveals that the predicted energy confinement quality is below 1 even at the highest pedestal pressure. The improvement in Q at higher pedestal density is due to the improved fusion power generation at the higher core density associated with higher pedestal density, not to an improved energy confinement quality.

Observation of a reduced-turbulence regime with boron powder injection in a stellarator

In state-of-the-art stellarators, turbulence is a major cause of the degradation of plasma confinement. To maximize confinement, which eventually determines the amount of nuclear fusion reactions, turbulent transport needs to be reduced. Here we report the observation of a confinement regime in a stellarator plasma that is characterized by increased confinement and reduced turbulent fluctuations. The transition to this regime is driven by the injection of submillimetric boron powder grains into the plasma. With the line-averaged electron density being kept constant, we observe a substantial increase of stored energy and electron and ion temperatures. At the same time, the amplitude of the plasma turbulent fluctuations is halved. While lower frequency fluctuations are damped, higher frequency modes in the range between 100 and 200 kHz are excited. We have observed this regime for different heating schemes, namely with both electron and ion cyclotron resonant radio frequencies and neutral beams, for both directions of the magnetic field and both hydrogen and deuterium plasmas.

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

Advanced operation scenarios such as high poloidal beta (β P) or high q min are promising concepts to achieve the steady-state high-performance fusion plasmas. However, those scenarios are prone to substantial Alfvénic activity, causing fast-ion transport and losses. Recent experiments with the advanced operation scenario on KSTAR tokamak have shown that the electron cyclotron current drive (ECCD) is able to mitigate and suppress the beam-ion driven toroidal Alfvén eigenmodes (TAEs) for over several tens of global energy confinement time. Co-current directional intermediate off-axis ECCD lowers the central safety factor slightly and tilts the central q-profile shape so that the continuum damping in the core region increases. Besides, the rise of central plasma pressure and increased thermal-ion Landau damping contribute to TAE stabilization. While the TAEs are suppressed, neutron emission rate and total stored energy increase by approximately 45% and 25%, respectively. Fast-ion transport estimated by TRANSP calculations approaches the classical level during the TAE suppression period. Substantial reduction in fast-ion loss and neutron deficit is also observed. Enhancement of fast-ion confinement by suppressing the TAEs leads to an increase of non-inductive current fraction and will benefit the sustainment of the long-pulse high-performance discharges.

Dynamics between toroidal Alfvén eigenmode evolution and turbulence suppression under resonant magnetic perturbations on EAST

Since Alfvén activity and turbulence are ubiquitous in magnetically confined plasma, it is important to understand the possible roles Alfvén activity have in the nonlinear evolution of turbulence. The designed experiments in low collisionality are dedicated to studying the dynamics between turbulence and toroidal Alfvén eigenmodes (TAEs), and assessing the multi-scale physics on the long-term scale behavior of fusion plasma. In TAEs (f ∼ 200 kHz, n = 1) mitigation experiments under resonant magnetic perturbations (RMP, n upper = 2 and n lower = 3), there is a long-term (∼500 ms) quasi-stationary state after RMP rapidly reduces the TAEs amplitude four times. Turbulence suppression (2.0 < kρ s < 3.8) and low-frequency zonal flow (LFZF) generation are observed in this period. Similar experiments show that energetic particles (EPs) may act as a mediator of the cross-scale interactions and are beneficial for turbulence suppression and LFZF generation. Besides the synchronous couplings of turbulence (2.0 < kρ s < 3.8) and TAEs, TAEs and LFZF are observed. The dynamics between turbulence and TAEs provides an idea for synchronous control of TAEs and turbulence, and the resulting EPs confinement improvement, T e increase, T i increase and plasma stored energy increase are favorable for plasma performance.

Impact of divertor closure on edge plasma behavior in EAST H-mode plasmas

A series of H-mode discharges have been conducted in the EAST tokamak to study the effect of divertor closure on divertor neutral distribution and edge plasmas by scanning the location of the outer strike point. When the outer strike point moves close to the corner within ∼, the gauge in upper sub-divertor shows that the neutral pressure increases, and the reciprocating probe at outer mid-plane indicates that electron temperature decreases and electron density increases in the scrape-off layer (SOL). In the meantime, the tungsten impurity concentration and radiation power in the main plasma decrease remarkably, while the main plasma density and stored energy increase slightly. SOLPS-ITER simulation without particle drifts is performed to better understand the impact of divertor closure. The simulation clearly demonstrates that a more closed divertor produces more neutrals around the corner with the increase of electron density and the decrease of electron temperature in the SOL, consistent with experimental results. Furthermore, more neutrals escape the divertor region and penetrate into the pedestal region, which induces more pedestal fuelling, increasing pedestal electron density. EAST will upgrade the lower divertor with a more closed geometry. These results provide important guidance for the upcoming upgrade.

Thermal Stability of Ultrafine-Grained Pure Titanium Processed by High-Pressure Torsion

High-pressure torsion (HPT) was conducted under 6.0 GPa on commercial purity titanium up to 10 turns. An ultrafine-grained (UFG) pure Ti with an average grain size of ~96 nm was obtained. The thermal properties of these samples were studied by using differential scanning calorimeter (DSC) which allowed the quantitative determination of the evolution of stored energy, the recrystallization temperatures, the activation energy involved in the recrystallization of the material and the evolution of the recrystallized fraction with temperature. The results show that the stored energy increases, beyond which the stored energy seems to level off to a saturated value with increase of HPT up to 5 turns. An average activation energy of about 101 kJ/mol for the recrystallization of 5 turns samples was determined. Also, the thermal stability of the grains of the 5 turns samples with subsequent heat treatments were investigated by microstructural analysis and Vickers microhardness measurements. It is shown that the average grain size remains below 246 nm when the annealing temperature is below 500 °C, and the size of the grains increases significantly for samples at the annealing temperature of 600 °C.

Investigation of recrystallization kinetics in hot-rolled Mg-La alloy using differential scanning calorimetry technique

In the present study the kinetics of recrystallization phenomenon of hot-rolled Mg-1.33La (wt.%) alloy was investigated using differential scanning calorimetry (DSC) analysis. The alloy was hot-rolled at 693 K to 20 and 50 % of thickness reduction. The DSC experiments results showed that the peak of recrystallization process ranged from 441.9 ± 2.0–497.8 ± 4.0 K and increased with increasing heating rate. The activation energy evaluated through the non-isothermal DSC treatment ranged from 93.3 ± 2.1–116.6 ± 2.6 kJ mol−1 and correlates well with the increase of stored energy during the deformation processing. The Avrami exponent of recrystallization was found close to 0.6 which indicates that the recrystallization preferentially occurred along grain boundaries and within deformation features such as twins.

Effect of the Mg contents on the annealing mechanism and shear texture of Al–Mg alloys

As conventional Al–Mg alloys have a high stacking fault energy (SFE), a copper type texture evolves when it is deformed and annealed at ambient temperatures. Generally, the SFE decreases as the Mg content increases. If the SFE decreases sufficiently, the microstructure texture can change from copper to brass type. To achieve good formability with an optimal microstructure texture, severe plastic deformation (SPD) processes have been studied, and these processes mainly have shear deformation mode. As a type of SPD test, a torsion test is a method to obtain data for shear deformed materials. In this study, the effects of the Mg content on the evolution of shear and annealing textures of Al–Mg alloys were investigated using torsion tests. Al–6Mg and Al–9Mg alloys were deformed to a strain of 0.35 at a strain rate of 0.1 s−1 at room temperature. After the materials were torsioned, an annealing process was conducted at 300 °C for 0–60 min for the deformed specimens. The electron backscattered diffraction technique was used to evaluate the microstructural texture of the samples after the suggested steps. As the Mg content increases under the same processing condition, a transition from copper to brass type was observed. A high Mg content resulted in an increase in stored energy. The variation in stored energy is related directly to the evolution of the annealing texture and its mechanism.

H-mode pedestal improvements with neon injection in DIII-D

Improvements in the H-mode pedestal pressure and global energy confinement were observed on DIII-D with both 3 and 6 MW of neutral beam (NBI) heating with neon injection. The pedestal pressure increased, primarily associated with a significant increase in the pedestal density with a relatively smaller decrease in the pedestal temperature. At the same neon injection rate, a rapid decrease in edge localized mode (ELM) frequency and ∼35% increase in plasma stored energy were observed in the 3 MW discharge, while in the 6 MW discharge, the ELM frequency was gradually decreased and the plasma stored energy gradually increased by up to 20%. The measured pedestal widths from both 3 and 6 MW discharges matched the EPED1.0 width scaling, , within 20% deviations before and after neon injection. The peeling-ballooning mode (PBM) stability analysis showed that after neon injection, the ballooning stability boundary was increased, while the peeling stability boundary only dropped once the neon level was relatively high. The ballooning stability boundary increase with neon injection is consistent with increase of the ion diamagnetic stabilization (i.e. including the contribution from carbon, neon as well as deuterium ions) which is used in the criterion to determine when the calculated linear growth rates of PBM are unstable. Consequently, the new ELITE computed PBM boundaries were more consistent with the operating points than when only deuterium was included. This in turn indicates that the impurity may help to improve pedestal pressure through affecting ion diamagnetic frequency in the pedestal region, which could positively lead to the ballooning stability boundary extension.

Study of core plasma rotation characteristics of RF-heated H-mode discharges on experimental advanced superconducting tokamak

RF-heated H-mode plasmas are readily achieved with lower hybrid current drive and ICRF heating on experimental advanced superconducting tokamak (EAST). Characteristics of H-mode plasma rotation are studied, including the behaviors for non-stationary and stationary H-mode discharges. Experimental results indicate that substantial co-current core rotation increment is observed at L-H transition. For non-stationary discharges with multiple L-H transitions, central plasma rotation varies as the plasma enters and exits the H-mode phase. Rotation increase over L-H transition is linearly correlated with plasma stored energy for both edge localized mode (ELM)-free phases and phases with type-III ELMs. For stationary H-mode discharges with type-III ELMs, core plasma rotation profile is elevated and remains stable during the H-mode phase, although the occurrence of ELMs tends to slow down the core rotation, especially for type-I ELMs where the entire core profiles are affected. Evolution of plasma rotation is fitted with a source-free transport equation and it is found that the momentum transport is dominated by diffusion and explains the flat profile in the core. Based on the Rice scaling and for the same stored energy increase, smaller increase in the core rotation is observed for H-mode discharges with type-III ELMs than for ELM-free discharges. A linear fit indicates that the slope is 75% larger for the ELM-free discharges data.

(Invited) The Scalability of Accelerating Rate Calorimetry (ARC) with State of Charge and Capacity

Sandia National Laboratories has used Accelerating Rate Calorimetry (ARC) as a means to evaluate and compare the total energies of thermal runaway. This has been an invaluable tool for evaluating the behavior of new chemistries as they become available in commercial and prototype cells. However, this testing has typically been performed in 18650 cells of ~1-1.5 AH and on cells at 100% state of charge. This has been invaluable for the evaluation and comparison of the thermal runaway of different lithium ion battery chemistries, however it leaves open questions as how changes to energy density, cell size and state of charge impact the results from calorimetry testing. This work examines the results of accelerating rate calorimetry testing on different lithium ion cathode chemistries (LCO, NCA, NMC, LFP) different formats (18650, pouch, large format cylindrical) and states of charge to understand how ARC results are impacted by both energy density and total energy. Also studied are how thermal runaway is impacted by energy in general, looking at both the total energy release during thermal runaway as well as the peak heating rates observed. While the total energy release is expected to correlate with the stored energy of the cell, the peak heating rates will impact how cells might behave in a variety of conditions. This has implications for battery design, as data suggests that even cells at relatively low states of charge may be hazardous if sufficiently insulation allows self-heating to occur even at relatively low rates; figure 1 shows data collected on 14 AH pouch cells summarizing the observed runaway energies and peak heating rates. This shows a relatively linear response as the stored energy increases, however an exponential response is observed with respect to state of charge. While this affirms the conventional wisdom that low state of charge cells are unlikely to go into thermal runaway in most environments, we can still see significant stored energy even at relatively low states of charge. The right conditions may still make these cells hazardous, making it important to fully understand the thermal decomposition of cells under a wide variety of conditions. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Figure 1 Comparison of total enthalpy observed during runaway of a 14 AH pouch cell to the peak heating rates at various states of charge. Figure 1

Real-time reduction of tungsten impurity influx using lithium powder injection in EAST

We report the first successful use of solid material injection, in powder form, to reduce core tungsten impurities in EAST discharges with tungsten divertor plasma-facing components. Tungsten is the leading plasma-facing material for use in ITER as well as future fusion devices. However, tungsten sometimes accumulates in the plasma core of fusion devices, which is an impediment to the achievement of high-power, long-pulse H-modes. In this work, tungsten impurity influx from the tungsten divertor was reduced by real-time injection of lithium powder into EAST discharges. An increase in stored energy and confinement accompanied the sharp reduction of core tungsten with real-time lithium powder injection in L-mode discharges. In H-mode discharges, real-time lithium powder injection reduced the tungsten core impurity emission while also mitigating ELMs. During powder injection, the divertor electron temperature was reduced, which reduced the tungsten source. The tungsten impurity emission remained low in discharges even after active lithium injection was terminated, a signature of improved and lasting wall conditioning in the tungsten divertor.

Plasma shaping and its impact on the pedestal of ASDEX Upgrade: edge stability and inter-ELM dynamics at varied triangularity

The plasma shape, in particular the triangularity (δ), impacts on the pedestal stability. A scan of δ including a variation of heating power (Pheat) and gas puff was performed to study the behaviour of edge localised modes (ELMs) and the pre-ELM pedestal stability for different plasma shapes. Generally, at higher δ the pedestal top electron density (ne) is enhanced and the ELM repetition frequency (fELM) is reduced. For all δ, the pedestal top ne is already fully established to its pre-ELM value during the initial recovery phase of the ne pedestal, which takes place immediately after the ELM crash. The lowering of the fELM with increasing δ is related to longer pedestal recovery phases, especially the last pre-ELM phase with clamped pedestal gradients (after the recovery phases of the ne and electron temperature (Te) pedestal) is extended. In all investigated discharge intervals, the pre-ELM pedestal profiles are in agreement with peeling–ballooning (PB) theory.Over the investigated range of δ, two well-separated fELM bands are observed in several discharge intervals. Their occurrence is linked to the inter-ELM pedestal stability. In both kinds of ELM cycles the pedestal evolves similarly, however, the ‘fast’ ELM cycle occurs before the global plasma stored energy (WMHD) increases, which then provides a stabilising effect on the pedestal, extending the inter-ELM period in the case of the ‘slow’ ELM cycle. At the end of a ‘fast’ ELM cycle the ne profile is radially shifted inwards relative to the ne profile at the end of a ‘slow’ ELM cycle, leading to a reduced pressure gradient. The appearance of two fELM bands suggests that the pedestal becomes more likely PB unstable in certain phases of the inter-ELM evolution. Such a behaviour is possible because the evolution of the global plasma is not rigidly coupled to the evolution of the pedestal structure on the timescales of an ELM cycle.

On the stored energy evolution after accumulative roll-bonding of invar alloy

The evolution of stored energy associated with Brass {110}<112>, Copper {112}<111>, S {231}<346> and Cube {001}<100> texture components of Fe-36Ni (wt.%) Invar alloy after accumulative roll-bonding (ARB) processing up to 6 cycles was investigated using two methods: Neutron Diffraction peak broadening analysis and Kernel Average Misorientation (KAM) in an electron backscatter diffraction (EBSD). Both methods evidence the stored energy evolution variation as ECopper > ES > EBrass > ECube. The stored energy increases first with strain up to 3 cycles and then decreases and then slightly rises up again between 4 and 6 cycles but with a trend towards stabilization. The overall evolution of the stored energy versus strain was related to the dislocation density and substructure evolution as well as recovery process. The small increase of the stored energy at high deformation levels is due to the production of new dislocations. Comparisons between results obtained with the two methods and with Dillamore approach show that Geometrically Necessary Dislocations (GND) dislocations in the cells/sub-grains walls are the principal contributor to the stored energy of the alloy.